During a complex revision total knee arthroplasty, the surgeon inadvertently cuts an excessive amount of bone from the distal femur. To compensate and tighten the extension gap, a very thick tibial polyethylene insert is utilized. This cascade effectively elevates the joint line proximally. What is the most profound functional consequence of this isolated joint line elevation?

Explanation:
The correct option is a. Elevating the joint line fundamentally alters knee kinematics. Because the collateral ligaments (MCL and LCL) attach to the epicondyles (which are now further away from the elevated tibial surface when the knee flexes), elevating the joint line makes the collateral ligaments relatively lax as the knee moves from extension into flexion. This results in profound mid-flexion instability (the knee feels perfectly tight straight, but wobbles dangerously at 30-60 degrees). Additionally, because the patellar tendon length is fixed at the tibial tubercle, moving the femoral articular surface proximally means the patella now articulates abnormally low on the new joint line, creating a severe functional patella infera (baja) that severely restricts terminal flexion. Reference: Figgie HE et al. The influence of tibial-patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg Am.